1. Field of the Invention
This invention relates to optical gauges, and more particularly to optical gauges for determining the level of a medium in a container, such as the level of fuel in a fuel tank.
2. Description of the Related Art
Prior art liquid level gauges, such as fuel gauges for motor vehicles, usually include a float that rides on an upper surface of the fuel in a fuel tank. The float is typically connected to one end of a pivot arm while the other end of the pivot arm typically includes a wiper mechanism that brushes against a resistor strip when the arm is rotated due to a change in fuel level in the tank. The wiper mechanism, when rotated, causes a change in electrical resistance which is displayed at a convenient location in the passenger compartment of the vehicle. Ideal fuel level measurement conditions would require the vehicle to remain stationary or travel along a flat, horizontal surface at a constant velocity in order to eliminate any fuel sloshing in the tank. However, it is not possible to achieve ideal measurement conditions in the real world. Variations in velocity, acceleration and centrifugal forces, road roughness, response of the vehicle's suspension, and other factors may cause the fuel to slosh in the tank in an unpredictable manner. When sloshing occurs, float movement becomes erratic and may result in false measurements of the actual fuel level in the tank.
Moreover, liquid level gauges with moving parts that are linked together, such as float and pivot arm assemblies, resistance strips, etc., are subject to wear. Worn parts may result in mechanical and/or electrical breakdown of the gauge or, at the very least, inaccurate liquid level detection.